Is it cruel to find out? I hope not. I profited from the ultra-hot sunny weather to bring a pail of organic-laden water with larvae happily snapping around, onto my back patio in full sun. I then ladled some water with larvae into a plate with about 3/8″ of water. You see both in the photo:
Within 25 minutes, all larvae in the plate at 115F had expired. Within an hour and a half, almost all those in the pail had kicked the bucket, at 100F surface temperature. (Larvae have to spend much of their time at the surface to breathe, though they dive if provoked.)
At the right of the photo you see the screen that after the experiment I put over the bucket, to be sure no adult mosquitoes can emerge, but I think by tomorrow any surviving larvae probably will be done for too.
This little exercise has practical value: we can conclude that in weather like this, larvae will not survive in a shallow pool on a flat roof (similar to the plate) and that even in deeper water exposed to the sun as in a roofline gutter, they have little chance.
Of course, we shouldn’t take it for granted and, bearing in mind that 100F is not normal here, we should keep flat roofs and gutters free of stagnant water!
Next afternoon update: there are in fact a few survivors, despite similar air (95) and water (100+) temps. Survival of the fittest, I guess. Those I spotted are on the small side; maybe the closer they are to pupating, the less resistant to heat?
Last observation: Air this hot deters mosquitoes on the wing. We know they like shade; maybe they shrivel up in sun over 90 degrees? Too bad that sunny and 95 are not great conditions for humans to be out in the garden either!